Adapting Wepp (Water Erosion Prediction Project) for Forest Watershed Erosion Modeling

摘要

Recently, there has been an increasing public concern for forest stream pollution by excessive sedimentation resulting from human activities. Adequate and reliable erosion simulation and prediction tools are urgently needed for sound forest resources management. Computer models for predicting watershed runoff and erosion have been developed during the past. These models, however, are often limited in their applications due to limited understanding and inappropriate representation of the hydrological processes involved. The Water Erosion Prediction Project (WEPP) watershed model has demonstrated its usefulness in certain forest applications such as modeling erosion from a segment of insloped or outsloped road, harvested units, and burned units. Nevertheless, when used for modeling water flow and sediment discharge from a forest watershed of complex topography and channel systems, WEPP consistently underestimates these quantities, in particular, the water flow at the watershed outlet. The main purpose of this study is to improve the WEPP watershed model such that it can be applied to adequately simulate forest watershed hydrology and erosion. The specific objectives are to: (1) identify and correct WEPP algorithms and subroutines which inappropriately represent forest watershed hydrologic processes; and (2) verify the modified model. In modifying the WEPP model, changes were primarily made in the approach to, and algorithms for modeling deep percolation of soil water and subsurface lateral flow. The modified model was then applied to a conceptual forest watershed in the Pacific Northwest with local data. The modeling results were compared with those obtained by using the original model. Conclusions of this study include: (1) compared to the original model, the modified WEPP more realistically and properly represents the hydrologic processes in a forest setting; and (2) application of the modified model to the conceptual watershed produced satisfactory results, demonstrating the adequacy of the model modifications.